The studies proposed in this application are based on the premise that recurring seizures in early-life contribute to cognitive deficits in children with intractable epilepsy. Animal models of early-onset epilepsy have advanced our understanding of the effects seizures have on brain development. Several laboratories have shown that infantile recurring seizures can produce deficits in learning and memory. These effects are not explained by the death of neurons. However, dendritic abnormalities in hippocampal pyramidal cells - including a reduction in dendritic branching - have been reported. Consistent with this observation are recent findings of decreased expression of dendritic glutamatergic postsynaptic proteins. In the Progress Report, we show that these effects are reproduced in an in vitro model of developmental epilepsy, where epileptiform activity is induced in hippocampal slice cultures by treatment with a GABAa receptor antagonist. During the course of these studies evidence began to accumulate that the primary deficit produced by epileptiform activity was not on glutamatergic synaptic transmission but on dendrites. Further studies confirmed this and showed that chronic disinhibition actually prevents the growth of dendrites and in a NMDA receptor dependent manner. Using our in vitro model, additional studies explored molecular mechanisms responsible for the suppression of dendrite growth. Results showed that activity through a signaling cascade previously implicated in dendrogenesis, the MAPK-CREB signaling pathway, is shut-off by chronic network hyperexcitability. Our most recent results have confirmed 2 critical aspects of our in vitro data in an in vivo model. We have found that a NMDA receptor antagonist blocks seizure-induced decreases in the expression of dendritic proteins and that signaling in the MAPK-CREB pathway is dramatically and persistently depressed by recurrent seizures. Based on these results we hypothesize that recurrent seizures in early-life suppress the growth of dendrites and the shut-off in signaling to CREB contributes to dendrite growth suppression. To test these hypotheses seven specific aims are proposed. Using the Flurothyl Model we plan to directly demonstrate that recurrent seizures suppress the growth of dendrites. Immunoblotting for dendritic proteins as well as dendrite reconstructions at numerous developmental time points will attempt to show that developmental increases in animals that have experienced seizures lag behind those observed in controls. Other studies in vitro and in vivo will set out to show that the shut-off in CREB signaling is an antecedent of and therefore potentially causative in growth suppression. Transfections of slice culture neurons with the constitutively active form of CREB are aimed at directly implicating a shut-off in CREB signaling in dendrite growth suppression. Experiments will also begin to explore the molecular basis of growth suppression by examining alterations in PKA function. By identifying the cellular and molecular events responsible for dendrite growth suppression, novel therapies may be developed to prevent learning deficits produced by recurring seizures. Children with severe epilepsy are often learning impaired. Similar observations have been made in young animals that have experienced seizures. Results suggest that developing neurons grow abnormally slow after seizures. We are studying why this happens so therapies can be developed to prevent learning disabilities. Children with severe epilepsy are often learning impaired. Similar observations have been made in young animals that have experienced seizures. Results suggest that developing neurons grow abnormally slow after seizures. We are studying why this happens so therapies can be developed to prevent learning disabilities.